The present invention relates to thermodynamic devices and, in particular, to thermodynamic devices having several liquid containers operating at different pressures, as is the case with heat pumps, for example.
European patent EP 2 016 349 B1 discloses a heat pump comprising a water evaporator, a compressor, and a liquefier. During heat pump operation, the pressure within the evaporator is set such that working fluid that is to be evaporated, such as water, for example, will evaporate at the temperature necessitated, which may be +10° C., for example. The compressor, which is configured as a continuous-flow machine having a radial impeller, compresses the steam and transports the compressed steam into a liquefier. Due to the steam compression, the temperature of the steam is increased from the temperature within the evaporator to a higher temperature, such as 40 or 50° C., for example. The heated steam will condense within the liquefier and thus heat the working fluid within the liquefier. When the heat pump is heating, the heat introduced into the liquefier by the compressed steam may be used for heating buildings. However, when the heat pump is cooling, the heat introduced into the liquefier will be discharged as waste heat, whereas the working fluid cooled by the evaporation within the evaporator will be used for cooling purposes.
On account of the heat pump operation, material is continuously transported forward from the evaporator into the liquefier. To ensure that the liquefier does not overflow, a drain is provided through which liquefied water is passed back toward the evaporator via a pump or a valve for pressure control.
As a pump or valve for pressure control, typical heat pumps comprise adjustable throttles so as to achieve conversion of high pressure within the liquefier to low pressure within the evaporator. The amount of working fluid that is transported back through the drain varies considerably since the working fluid that is transported forward also varies considerably due to the evaporation/compression/liquefying process. This is due to the fact that the heat pump varies as the power increases, or as the temperature spread, i.e. the temperature difference between the high temperature present within the liquefier and the low temperature present within the evaporator, increases. If a heat pump has to provide a large amount of power n order to achieve heating or cooling, more working fluid will be transported than if a heat pump has to provide little power in order to achieve heating or cooling. Therefore, the throttle is typically adjustable so as to be able to accommodate the wide range of different flows in the drain.
What is disadvantageous about this concept is the fact that the throttle, which even has to be adjustable, entails additional cost and additional losses in the heat pump process. In particular due to the spontaneous evaporation of the warm working fluid which typically takes place within such throttles, said warm working fluid passing into the low-pressure area, energy losses are generated and, additionally, noises are produced which contribute to the overall noise level of the heat pump. In particular when a heat pump is intended for mass utilization, which is the case with typical heat pumps, the cost for said additional component and the necessitated control also play a part that is not to be underestimated; additionally, the susceptibility to failure is also to be mentioned.